Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

Women told to eat healthy low-density foods, especially fresh fruits and vegetables, lose more weight than those told to cut fat, according to research unveiled Wednesday.

A related study showed that Americans who ate more of these foods consumed fewer calories and were somewhat healthier than those who didn't — even though they ate more total food.

In the first study, two groups of obese but otherwise healthy women got regular dietary advice for a year. One group was told what to avoid in order to reduce the amount of fat in their diets. The other got the reduced-fat advice, but was also given positive messages — suggestions of healthy, water-rich foods they could add to their diets.

Video: Low-density diets
They were specifically directed to items with a low energy density, or ratio of calories to mass, and high water content; not only produce but soups, legumes and cooked grains like oats and brown rice.

Both groups lost weight. But after six months, the reduced-fat group had lost 14.7 pounds, while the energy-density group had lost 20.7 pounds.

"We didn't give them all this 'Don't eat this, don't eat that,'" Penn State nutrition sciences professor Barbara Rolls, who directed both studies, told MSNBC.com. "Human nature is, we really don't like to be told we can't have things."

Feeling full with fewer caloriesWater-rich foods' value rests in the ability to eat more of them and feel fuller without packing in extra calories. While other studies have shown the efficacy of short-term diets featuring these foods, nutrition researchers said these findings help prove the long-term effects and fill in gaps in current research.

"It provides additional support that folks can actually eat more food and lose weight if they choose foods low in calories," said Gail Woodward-Lopez, associate director of the Center for Weight and Health at the University of California, Berkeley. "That's wonderful that they did both a longer-term intervention study and an observational study."

All the women were told to seek out leaner cuts of meat and poultry and to cook using healthier methods — grilling rather than frying. They were instructed about exercise and long-term eating habits. The reduced-fat group was given additional health advice, while the energy-density group learned how to devise menus of water-rich foods, Penn State researcher Julie Ello-Martin said, such as grapes instead of raisins.

After a year, both groups gained back a few pounds, but were more successful than usual in keeping off weight. The energy-density group kept off an average 18 pounds, while the reduced-fat group averaged 14 pounds.

"In most weight-loss studies, you really see people rebounding, and we didn't see that in this study," said Ello-Martin, who conducted the study.

The virtues of both approaches dovetails with
findings this week
that, on a long-term basis, low-fat approaches beat out popular low-carb. Proponents of Atkins and other low-carb plans defended their efforts, but face growing backlash from nutritionists.

Healthier habitsIn the other Penn State study, researchers reviewed federal data from 1994 to 1996 on the eating habits of 7,500 individuals. They found that people who ate more low energy-density foods ingested fewer calories and fat, and had a lower body mass index, than those who ate denser foods.

The low-density group consumed 1,850 calories daily, versus 2,193 for the high-density group, including fewer calories from both food and beverages, including 29.6 percent of their calories from fat, versus 36.7 percent. They consumed more protein, carbohydrates, fiber, fruits and vegetables than their high-density counterparts, and had a BMI of 25.5, versus 26.1.

Significantly, while both groups consumed about the same total weight of food and drinks, low-density eaters ate more food by weight, drank less and got fewer calories from beverages — a key finding for dieters trying to cut caloric sodas from their routines.

Both studies were presented at a meeting of the North American Association for the Study of Obesity in Las Vegas. Rolls' group also revealed a study this week in which
they removed
800 calories from some women's' daily diets with few complaints.

Conflicting messagesThe latest research underscores the conflicting messages Americans often receive about their weight. With two-thirds of Americans either overweight or obese, public officials and nutritionists consider obesity an epidemic.

Some food companies are looking to promote healthier products; McDonald's and others are touting new salad entrees. Others are openly defiant. Fast-food chain Hardee's
this week unveiled
its new 1,420-calorie Monster Thickburger.

Though "water weight" is often derided, it can effectively help people feel full. Few people can eat more than one buttered baked potato, while many of us easily scarf down several potatoes worth of fries, which replace water with fat, or potato chips, which remove even more water, Woodward-Lopez noted.

Though the latest research mostly reaffirms old sensibilities about eating well, it backs up the strategies with hard data, which researchers believe will be crucial to changing Americans' eating habits.

"This is old news in a sense, except the work is being done much more carefully to prove the obvious," said New York University nutrition science professor Marion Nestle. "That's what makes this work important, even though the results of it seem so intuitive."